Cellular communication networks typically include a number of base stations, where each base station serves a “cell”, and multiple mobile units, (referred to herein as user equipment (UEs)), that may move through and between the cells. The 3rd Generation Partnership Project (3GPP) is presently defining various communication standards and protocols, including standards and protocols for the emerging next generation, LTE (Long Term Evolution) Advanced cellular telecommunication standard.
Cellular communications systems may require mobile units to communicate regularly with the base stations, including during active voice or data calls, as well as when not actively engaged in a call. This regular communication utilizes battery power and may drain power from the battery. In LTE and other standards, a UE may periodically shut down various receiver modules when not needed, thereby entering an “idle” or “standby” mode, to reduce its power consumption. Entering the idle or standby mode is also called “going to sleep”.
However, even when in idle mode, the UE still needs to periodically wake up, for example, to monitor signals that are transmitted at specific times, called paging slots, and to determine if it needs to fully wake up and receive a call. The UE may also utilize paging slots to receive additional signals, to update its knowledge of the network, to change cell information if the UE is moving, etc. In LTE, for instance, the periodicity of paging slots is up to 2.56 sec.
When in idle mode, a UE may turn off various components other than those components needed to maintain a timing synchronization between the UE and a network. A “slow clock unit” in the UE typically is responsible for waking the UE after a sleep period. It may be based on a relatively inexpensive and power efficient crystal. However, slow clock units may be somewhat inaccurate, which might result in the UE waking up at incorrect times. For timing correction the UE may use known signals that the base station periodically transmits. Normally, the UE wakes up the time tracking module with enough time to correct any timing errors before the expected receipt of the paging signal.